Weekly Scouting Report - July 22, 2014
I scouted soybeans this week and found bean leaf beetles. They are a quick little insect and very hard to find. As soon as they sense your presence, they fall to the ground. I entered the fields and immediately noticed leaf feeding. The feeding reminds me of what a shot gun blast would look like, having numerous small holes. I found many of them in the upper most node, feeding on the new growth. They like cooler weather and this cooler weather has them out more during the day. Late morning or early evening are normally the best time to find them. Economic threshold in the reproductive stage of the soybean (R1-R6) is 2-3 bean leaf beetles per plant. Insecticide application should be applied when beetles reach this level.
Adult bean leaf beetles are small insects about 1/5 inch in length. They often have four, large, quadrangular, black markings on the wing covers and a black or brown head. Occasionally these four rectangular marks are reduced to two, or they may be completely absent. The most constant identifying character for this beetle is the presence of a black triangle behind the neck. They come in a wide array of colors.
Direct injury results from bean leaf beetles feeding on soybean pods. This direct injury occurs an average rate of about two tenths of a pod per day. Bean leaf beetles also cause yield loss through injury by the transmission of bean pod mottle virus or by the secondary invasion of fungi.